A: The tracert mechanism of NE40E is that: NE40E sends 3 packets every time with hash mechanism base on 5 cell groups (source ip, destination ip, source port, destination port and ip protocol id).There are two next-hops in the example so the next-hop of sending tracert packets with 4 times and 12 packets totally are 1, 2, 1; 2, 1, 2; 1, 2, 1; 2, 1, 2; 1, 2, 1. (1 means 1st next-hop and 2 means 2nd one).1. NE40E sends 3 packets with TTL=1 in the first hop, and the next-hop routers receive and drop due to TTL=0 after TTL is decreased 1 by itself then one ICMP timeout echo is replied to souce, then the source prints the concerned log after it receives the ICMP timeout echo.

2. NE40E sends 3 packets with TTL=2 in the second hop, and the next-hop routers receive and forward it to its next-hop router after TTL is decreased 1 by itself, then the next next-hop receives and drops due to TTL=0 after TTL is decreased 1 by itself then one ICMP timeout echo is sent to souce, then the source prints the concerned log after it receives the ICMP timeout echo.3. Similar as 1st and 2nd one.4. Similar as 1st and 2nd one.So the correct route paths in the example are those two ones.172.31.254.106--> 172.31.252.193-->172.31.1.21-->172.31.1.50 172.31.252.189--> 172.31.1.17 -->172.31.1.46-->172.31.254.50

Root Cause

A: The tracert mechanism of NE40E is that: NE40E sends 3 packets every time with hash mechanism base on 5 cell groups (source ip, destination ip, source port, destination port and ip protocol id).There are two next-hops in the example so the next-hop of sending tracert packets with 4 times and 12 packets totally are 1, 2, 1; 2, 1, 2; 1, 2, 1; 2, 1, 2; 1, 2, 1. (1 means 1st next-hop and 2 means 2nd one).1. NE40E sends 3 packets with TTL=1 in the first hop, and the next-hop routers receive and drop due to TTL=0 after TTL is decreased 1 by itself then one ICMP timeout echo is replied to souce, then the source prints the concerned log after it receives the ICMP timeout echo.

2. NE40E sends 3 packets with TTL=2 in the second hop, and the next-hop routers receive and forward it to its next-hop router after TTL is decreased 1 by itself, then the next next-hop receives and drops due to TTL=0 after TTL is decreased 1 by itself then one ICMP timeout echo is sent to souce, then the source prints the concerned log after it receives the ICMP timeout echo.3. Similar as 1st and 2nd one.4. Similar as 1st and 2nd one.So the correct route paths in the example are those two ones.172.31.254.106--> 172.31.252.193-->172.31.1.21-->172.31.1.50 172.31.252.189--> 172.31.1.17 -->172.31.1.46-->172.31.254.50